Any person who does that to their child does not deserve children.
So none.
It's not something I would do to one of my kids. Mostly because is hasn't been necessary. Also, I don't see that it is particularly bad either. We don't know what the kid did or how far off the rails he was going.
We also don't know how long this punishment lasted - whether the kid was forced to go out like that for weeks or if the parents then shaved off the rest of his hair after it actually sunk in. could be the kid just went to school the next day sporting a cool shaved head.
This is a non-violent form of punishment. It is not a beating. It certainly IS something the kid would not want to happen again. Maybe the parents have been trying time-outs but the kids just not been reacting to them the way many kids do.
It's easy to judge other parents. Especially easy for those people that don't have children. At the end of the day, if other avenues have been explored, other forms of non-violent punishment are not working, you do actually have to use your imagination to figure out just what it will take to get a child to back down WITHOUT hitting them.
Not that I'm totally against smacking kids - just that for various practical reasons, it's a tougher form of punishment to implement than something that pisses them off severely.